1. Field of the Invention
The present invention relates to a write head with all metallic laminated pole pieces and, more particularly, to such a write head wherein alternate ferromagnetic films in each pole piece have at least partial flux closure for minimizing domain walls in the pole pieces and increasing a frequency response of the write head.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
A write head typically employs ferromagnetic first and second pole pieces which are capable of carrying flux signals for the purpose of writing magnetic impressions into a track on a magnetic medium, such as a rotating magnetic disk. Each of the first and second pole pieces has a yoke region which is located between a pole tip region and a back gap region. The pole tip region is located at the ABS and the back gap region is spaced from the pole tip region at a recessed location within the write head. At least one coil layer is embedded in an insulation stack which is located between the first and second pole pieces in the yoke region. A nonmagnetic write gap layer is located between the pole tip regions of the first and second pole pieces. The thinner the thickness of the write gap layer, the greater the number of bits the write head can write into the track of a rotating magnetic disk. The first and second pole pieces are magnetically connected at the back gap. Processing circuitry digitally energizes the write coil which induces flux into the first and second pole pieces so that flux signals bridge across the write gap at the ABS to write the aforementioned magnetic impressions or bits into the track of the rotating disk. The second pole piece has a second pole piece yoke (P2 yoke) which is magnetically connected to the second pole tip (P2 tip) and extends to the back gap for connection to the first pole piece.
A write head is typically rated by its areal density which is a product of its linear bit density and its track width density. The linear bit density is the number of bits which can be written per linear inch along the track of a rotating magnetic disk and the track width density is the number of tracks that can be written per inch along a radius of the rotating magnetic disk. The linear bit density is quantified as bits per inch (BPI) and the track width density is quantified as tracks per inch (TPI). As discussed hereinabove, the linear bit density depends upon the thickness of the write gap layer. The track width density is directly dependent upon the width of the second pole tip at the ABS. Efforts over the years to increase the areal density of write heads have resulted in computer storage capacities increasing from kilobytes to megabytes to gigabytes.
The first and second pole pieces are typically fabricated by frame plating. Photoresist is employed to provide the frame and a seed layer is employed to provide a return path for the plating operation. A typical sequence for fabricating a pole piece is to sputter clean the wafer, sputter deposit a seed layer, such as nickel iron, on the wafer, spin a layer of photoresist on the wafer, light-image the photoresist layer through a mask to expose areas of the photoresist that are to be removed (assuming that the photoresist is a positive photoresist), develop the photoresist to remove the light-exposed areas to provide an opening in the photoresist and then plate the pole piece in the opening up to a desired height.
The magnetic moment of each pole piece is parallel to the ABS and to the major planes of the layers of the write head. When a write current is applied to the coil of the write head the magnetic moment rotates toward or away from the ABS, depending upon whether the write signal is positive or negative. When the magnetic moment is rotated from the parallel position, magnetic flux fringes across the write gap layer between the first and second pole pieces impressing a positive or negative bit in the track of a rotating magnetic disk. Assuming a disk rotation sufficient to provide the aforementioned air bearing and a particular write signal frequency, the aforementioned linear bit density can be calculated. As the write current frequency is increased, the linear bit density is also increased. An increase in the linear bit density is desirable in order to increase the aforementioned areal density which provides a computer with increased storage capacity. Unfortunately, the write current density is limited by the domain walls in the first and second pole pieces. Because of the energy required to move the domain walls around, the domain walls reduce the write time of the flux within the pole pieces in response to the write current frequency. Accordingly, the domain walls lessen the amount of flux that bridges between the write gap and reduces the strength of the magnetic impression into the track of the rotating magnetic disk. This can be corrected in two ways. First, the write current frequency can be decreased and/or the write current can be increased. Unfortunately, a decrease in the write current frequency results in a decrease in the linear bit density of the write head, and an increase in the amount of write current increases the generation of heat within the write head. An increase in the heat of the write head can destroy the delicate read sensor and/or cause one or more layers to protrude at the ABS due to expansion of the insulation stack.
The present invention overcomes the aforementioned problem by making the first and second pole pieces a lamination of alternate ferromagnetic and nonmagnetic metal films. Each nonmagnetic metal film causes an antiferromagnetic coupling between ferromagnetic films adjacent thereto so that the adjacent ferromagnetic films are antiparallel exchange coupled for at least partial flux closure therebetween. In a preferred embodiment, each nonmagnetic film is composed of ruthenium (Ru) and each ferromagnetic film is composed of nickel iron (NiFe). It is important that each nonmagnetic film be sufficiently thin so as to cause the antiferromagnetic coupling between the adjacent ferromagnetic films. This thickness is preferably in a range from 5 xc3x85 to 20 xc3x85. Further, it is important that the adjacent ferromagnetic films have a thickness differential so that there is a uniaxial anisotropy HK to position the magnetic moment of the pole piece parallel to the ABS and the major planes of layers of the write head. The present invention enables the HK to be set at a desired amount so that each pole piece is highly responsive to the write current signal. Further, the invention enables the ferromagnetic and nonmagnetic metal films of each pole piece to be formed by plating or sputtering.
Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings.